In my U.S. Pat. No. 4,378,187 I disclose a quick acting nut assembly having a plurality of internally threaded segments held within a nut casing, the segments being resiliently biased in the radial inward direction. Parallel inclined surfaces on the axial ends of the segments are adapted to slide along similarly inclined surfaces in the interior of the casing. An externally threaded element is received in the bore defined by the segments, to mesh with the threads of the segments.
With this structure, axial forces in one axial direction on the externally threaded element urge the segments in the nut casing radially outward, to permit the threads on the threaded element to step in the axial direction past the threads of the segments, thereby to permit the threaded element to move axially, relatively rapidly and with minimum force. Axial forces on the threaded element in the opposite direction, however, urge the segments radially inward, to enable conventional cooperation between the threads of the segments and the threaded element.
Nut assemblies having split segments with inclined outer surfaces are also disclosed, for example, in U.S. Pat. Nos. 2,021,051 to Desbrueres, 2,896,496 to Jansen, 3,352,341 to Schertz and 3,695,139 to Howe.
In conventional threaded connections, as illustrated in FIG. 16, while the tip to root dimension of the bolt is substantially the same as that of the corresponding nut, the tip diameter of the bolt is substantially less (e.g. 1%) than that of the nut. As a consequence the loading zone of the threads of the nut and bolt is reduced. Since the cross-sectional area of the threads that is subject to shear loads is substantially less than the cross-sectional area at the roots of the threads, the load carrying capacity of the threads is reduced.